Published: 3 Sep 2024

Establishing Reference Ranges for Laboratory Tests

Reference Population Definition

The selection of reference populations is crucial for establishing reference ranges, considering factors that may impact test results: age, sex, race, overall health, and medical history.

Data Collection and Analysis

A large sample size (minimum of 120) of individuals matching the reference population profile is tested under standardized conditions. The results are analyzed to determine the middle 95% of the reference population's values, which constitute the reference range.

Derivation of Reference Ranges

Laboratories can obtain reference ranges from:

* Their own internal studies
* Test manufacturers
* External sources with existing patient data

Importance of Contextual Interpretation

Reference ranges are not synonymous with "normalcy." Results should be interpreted within the context of individual circumstances, including:

* Past medical history
* Current medications
* Results of other investigations

Statistical Basis of Reference Ranges

Reference Population Normal Distribution

In a "normal" population, test results are expected to distribute normally, with most values falling within the reference range.

Standard Deviation and Reference Range

The reference range is calculated by taking the average value of the reference population and adding or subtracting 2 standard deviations (SD). This means that approximately 5% of test results (1 in 20) will fall outside the reference range, even in a "normal" population.